C# DragRigidbody ArgumentException: get_main can only be called from the main thread

Question

I'm trying to convert DragRigidbody into C# and I've encountered a problem. when I clicked my left mouse button I get the following error ArgumentException: get_main can only be called from the main thread. Following that Unity freezes and crashes. So I couldn't read what was causing the error from the console. Any idea what is wrong with the script?

 using UnityEngine;
 using System.Collections;
 
 public class DragRigidbody : MonoBehaviour {
 
     public float spring = 50.0f;
     public float damper = 5.0f;
     public float drag = 10.0f;
     public float angularDrag = 5.0f;
     public float distance = 0.2f;
     public bool attachToCenterOfMass = false;
     public Camera mainCamera = Camera.main;
     public RaycastHit hit;
     private SpringJoint springJoint;
     
     void Update ()
     {
         // Make sure the user pressed the mouse down
         if (!Input.GetMouseButtonDown (0))
             return;
         
         // We need to actually hit an object
         if (!Physics.Raycast(mainCamera.ScreenPointToRay(Input.mousePosition), out hit, 100))
             return;
         // We need to hit a rigidbody that is not kinematic
         if (!hit.rigidbody || hit.rigidbody.isKinematic)
             return;
         
         if (!springJoint)
         {
             GameObject go = new GameObject("Rigidbody dragger");
             Rigidbody body = go.AddComponent ("Rigidbody") as Rigidbody;
             springJoint = go.AddComponent("SpringJoint") as SpringJoint;
             body.isKinematic = true;
         }
         
         springJoint.transform.position = hit.point;
         if (attachToCenterOfMass)
         {
             Vector3 anchor = transform.TransformDirection(hit.rigidbody.centerOfMass) + hit.rigidbody.transform.position;
             anchor = springJoint.transform.InverseTransformPoint(anchor);
             springJoint.anchor = anchor;
         }
         else
         {
             springJoint.anchor = Vector3.zero;
         }
         
         springJoint.spring = spring;
         springJoint.damper = damper;
         springJoint.maxDistance = distance;
         springJoint.connectedBody = hit.rigidbody;
         
         StartCoroutine ("DragObject", hit.distance);
     }
 
     void DragObject (float distance)
     {
         float oldDrag = springJoint.connectedBody.drag;
         float oldAngularDrag = springJoint.connectedBody.angularDrag;
         springJoint.connectedBody.drag = drag;
         springJoint.connectedBody.angularDrag = angularDrag;
         Camera mainCamera = Camera.main;
         while (Input.GetMouseButton (0))
         {
             Ray ray = mainCamera.ScreenPointToRay (Input.mousePosition);
             springJoint.transform.position = ray.GetPoint(distance);
         }
         if (springJoint.connectedBody)
         {
             springJoint.connectedBody.drag = oldDrag;
             springJoint.connectedBody.angularDrag = oldAngularDrag;
             springJoint.connectedBody = null;
         }
     }
 }

Answer 1

Best Answer

Answer by robertbu · May 14, 2014 at 06:34 AM

Problem #1, you need to move the initialization of this variable to Start(). So you will declare the variable:

  public Camera mainCamera;

Then you will add:

 void Start() 
 {
     mainCamera = Camera.main;
 }

Problem #2 is that you've removed the 'yield' from line 68. That's what is causing your script to hang Unity. So just below line 67, insert:

 yield return null;

Now that you are using 'yield', 'DragObject' needs to be and IEnumerator. So line 57 becomes:

 IEnumerator DragObject (float distance)

And I would change the StartCoroutine() call on line 54 to:

 StartCoroutine (DragObject(hit.distance));

Make these changes, and your code will work.

1 Show 2 · Share

Ochreous · May 14, 2014 at 07:13 AM 0

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Unity's no longer crashing but I'm still getting the same argument exception from the console

 using UnityEngine;
 using System.Collections;
 
 public class DragRigidbody : MonoBehaviour {
 
     public float spring = 50.0f;
     public float damper = 5.0f;
     public float drag = 10.0f;
     public float angularDrag = 5.0f;
     public float distance = 0.2f;
     public bool attachToCenterOfMass = false;
     public Camera mainCamera = Camera.main;
     public RaycastHit hit;
 
     private SpringJoint springJoint;
 
     void Start()
     {
         mainCamera = Camera.main;
     }
 
     void Update ()
     {
         // Make sure the user pressed the mouse down
         if (!Input.GetMouseButtonDown (0))
             return;
         
         // We need to actually hit an object
         if (!Physics.Raycast(mainCamera.ScreenPointToRay(Input.mousePosition), out hit, 100))
             return;
         // We need to hit a rigidbody that is not kinematic
         if (!hit.rigidbody || hit.rigidbody.isKinematic)
             return;
         
         if (!springJoint)
         {
             GameObject go = new GameObject("Rigidbody dragger");
             Rigidbody body = go.AddComponent ("Rigidbody") as Rigidbody;
             springJoint = go.AddComponent("SpringJoint") as SpringJoint;
             body.isKinematic = true;
         }
         
         springJoint.transform.position = hit.point;
         if (attachToCenterOfMass)
         {
             Vector3 anchor = transform.TransformDirection(hit.rigidbody.centerOfMass) + hit.rigidbody.transform.position;
             anchor = springJoint.transform.InverseTransformPoint(anchor);
             springJoint.anchor = anchor;
         }
         else
         {
             springJoint.anchor = Vector3.zero;
         }
         
         springJoint.spring = spring;
         springJoint.damper = damper;
         springJoint.maxDistance = distance;
         springJoint.connectedBody = hit.rigidbody;
         
         StartCoroutine(DragObject(hit.distance));
     }
 
     IEnumerator DragObject (float distance)
     {
         float oldDrag = springJoint.connectedBody.drag;
         float oldAngularDrag = springJoint.connectedBody.angularDrag;
         springJoint.connectedBody.drag = drag;
         springJoint.connectedBody.angularDrag = angularDrag;
         Camera mainCamera = Camera.main;
         while (Input.GetMouseButton (0))
         {
             Ray ray = mainCamera.ScreenPointToRay (Input.mousePosition);
             springJoint.transform.position = ray.GetPoint(distance);
             yield return null;
         }
         if (springJoint.connectedBody)
         {
             springJoint.connectedBody.drag = oldDrag;
             springJoint.connectedBody.angularDrag = oldAngularDrag;
             springJoint.connectedBody = null;
         }
     }
 }

robertbu · May 14, 2014 at 12:20 PM 1

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The exception is because you did not fully make the first change. Line 12 should be:

 public Camera mainCamera;

The whole issue was the assignment of Camera.main.

Answer 2

excellent. been looking for this. the old js script sucks. Final working code below:

 using UnityEngine;
 using System.Collections;
 
 public class dragRigidbody : MonoBehaviour {
 
     public float spring = 50.0f;
     public float damper = 5.0f;
     public float drag = 10.0f;
     public float angularDrag = 5.0f;
     public float distance = 0.2f;
     public bool attachToCenterOfMass = false;
     public Camera mainCamera;
     public RaycastHit hit;
 
     private SpringJoint springJoint;
 
     void Start()
     {
         mainCamera = Camera.main;
     }
 
     void Update ()
     {
         // Make sure the user pressed the mouse down
         if (!Input.GetMouseButtonDown (0))
             return;
 
         // We need to actually hit an object
         if (!Physics.Raycast(mainCamera.ScreenPointToRay(Input.mousePosition), out hit, 100))
             return;
         // We need to hit a rigidbody that is not kinematic
         if (!hit.rigidbody || hit.rigidbody.isKinematic)
             return;
 
         if (!springJoint)
         {
             GameObject go = new GameObject("Rigidbody dragger");
             Rigidbody body = go.AddComponent <Rigidbody>() as Rigidbody;
             springJoint = go.AddComponent<SpringJoint>() as SpringJoint;
             body.isKinematic = true;
         }
 
         springJoint.transform.position = hit.point;
         if (attachToCenterOfMass)
         {
             Vector3 anchor = transform.TransformDirection(hit.rigidbody.centerOfMass) + hit.rigidbody.transform.position;
             anchor = springJoint.transform.InverseTransformPoint(anchor);
             springJoint.anchor = anchor;
         }
         else
         {
             springJoint.anchor = Vector3.zero;
         }
 
         springJoint.spring = spring;
         springJoint.damper = damper;
         springJoint.maxDistance = distance;
         springJoint.connectedBody = hit.rigidbody;
 
         StartCoroutine(DragObject(hit.distance));
     }
 
     IEnumerator DragObject (float distance)
     {
         float oldDrag = springJoint.connectedBody.drag;
         float oldAngularDrag = springJoint.connectedBody.angularDrag;
         springJoint.connectedBody.drag = drag;
         springJoint.connectedBody.angularDrag = angularDrag;
         Camera mainCamera = Camera.main;
         while (Input.GetMouseButton (0))
         {
             Ray ray = mainCamera.ScreenPointToRay (Input.mousePosition);
             springJoint.transform.position = ray.GetPoint(distance);
             yield return null;
         }
         if (springJoint.connectedBody)
         {
             springJoint.connectedBody.drag = oldDrag;
             springJoint.connectedBody.angularDrag = oldAngularDrag;
             springJoint.connectedBody = null;
         }
     }
 }

C# DragRigidbody ArgumentException: get_main can only be called from the main thread

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